Current understanding of the mechanisms of dichromatic color vision (e.g., that is of retinal origin and involves the loss of one of the three normal photopigments), is based on human psychophysical data. The hypotheses derived from these data need to be tested at the anatomical level. Such a test is possible in the tree shrew, a prototypical primate, which is the only animal known to exhibit color vision similar to human deuteranopes. The goal of this project is to eliminate the input of the shortwavelength sensitive (i.e., "blue sensitive") cone system in the tree shrew. Since this animal has dichromatic color vision and an all-cone retina, the identification and functional elimination of the short-wavelength sensitive cone system would transform it into a cone monochromat. Such a preparation has not been available before, and would be an ideal model in which to study properties of cone function in general, as well as the underlying mechanisms of dichromatic color vision. Two promising new neuroanatomical techniques will be applied to the tree shrew: 1) selective degeneration of short-wavelength sensitive cones produced by exposure to intense blue light; and 2) selective staining of these cones by intravitreal injection of Procion yellow dye. If these applications prove successful a long-range research program, combining a continual neuroanatomical approach with complementary psychophysical methods, could be initiated. In such a program the spectral sensitivity of isolated cone systems could be determined in behaving animals and then be linked to the underlying anatomical structure and retinal distribution of the cones. Results would have obvious clinical relevance to the understanding and treatment of human color vision defects.